This invention generally relates to methods and apparatus for inserting sliders onto zippers for use in reclosable packaging, such as zippered bags or pouches. In particular, the invention relates to slider insertion devices incorporated in machines for making reclosable packages having slider-operated zippers.
Reclosable bags are finding ever-growing acceptance as primary packaging, particularly as packaging for foodstuffs such as cereal, fresh fruit and vegetables, snacks and the like. Such bags provide the consumer with the ability to readily store, in a closed, if not sealed, package any unused portion of the packaged product even after the package is initially opened.
Reclosable bags comprise a receptacle having a mouth with a zipper for opening and closing. In recent years, many zippers have been designed to operate with a slider mounted thereon. As the slider is moved in an opening direction, the slider causes the zipper sections it passes over to open. Conversely, as the slider is moved in a closing direction, the slider causes the zipper sections it passes over to close. Typically, a zipper for a reclosable bag includes a pair of interlockable profiled closure strips that are joined at opposite ends of the bag mouth. The profiles of interlockable plastic zipper parts can take on various configurations, e.g. interlocking rib and groove elements having so-called male and female profiles, interlocking alternating hook-shaped closure elements, etc. Reclosable bags having slider-operated zippers are generally more desirable to consumers than bags having zippers without sliders because the slider eliminates the need for the consumer to align the interlockable zipper profiles before causing those profiles to engage.
In one type of slider-operated zipper assembly, the slider straddles the zipper and has a separating finger or plow in the middle or at one end that is inserted between the zipper profiles to force them apart as the slider is moved along the zipper in an opening direction. The other end of the slider is sufficiently narrow to force the zipper profiles into engagement and close the zipper when the slider is moved along the zipper in a closing direction.
In the past, many interlocking closure strips were formed integrally with the bag making film, for example, by extruding the bag making film with the closure strips formed on the film. Such constructions, however, were limited by the conditions required to extrude both the film and zipper together. To avoid such limitations, many bag designs entail separate extrusion of the closure strips, which are subsequently joined to the bag making film, for example, by conduction heat sealing. These separate closure strips typically have flanges extending therefrom in such a way that the flanges can be joined to bag making film in order to attach the closure strips to the film. Until recently, slider-operated, separately extruded zippers used flange-type constructions.
An alternative zipper design is the so-called flangeless or string zipper, which has substantially no flange portion above or below the interlockable closure profiles. In the case of a string zipper, the bag making film is joined to the backs of the bases of the closure strips. String zippers can be produced at much greater speeds, allow much greater footage to be wound on a spool, thereby requiring less set-up time, and use less material than flanged zippers, enabling a substantial reduction in the cost of manufacture and processing.
Recently, slider-operated, separately extruded zippers that do not use flange-type constructions have been disclosed. U.S. patent application Ser. No. 10/367,450 discloses a reclosable bag in which respective marginal portions of the bag film are sealed to the backs of respective flangeless zipper strips. The resulting string zipper is actuated by means of a straddling-type slider having a plow that separates the zipper strips during opening. U.S. patent application Ser. No. 10/436,433 discloses methods and apparatus for manufacturing reclosable bags having slider-actuated string zippers, including methods and apparatus for inserting sliders with plows on string zippers. These methods and apparatus may also have application for inserting sliders with plows on flanged zippers or zippers that have been coextruded with the bag.
When inserting a slider having a plow on a zipper, the zipper section where the slider is inserted must be maintained in an open state to allow the slider plow to project between the zipper profiles, but at the same time the side walls of the slider must be able to pass over and straddle the zipper profiles. However, difficulties arise when one attempts to insert the closing end of a slider over an open zipper using an automated insertion device.
There is a continuing need for improved methods and apparatus for automated insertion of sliders with plows on zippers.